FISHERY BULLETIN: VOL. 72, NO. 4 



Circular - 

 Shelled 



Mid Asymmetric - 



Early 

 Asymmetric 



Crawling 

 (Settling) 



Branched 

 Cepholic Tentocle 



Mid Cepholic _ 

 Tentacle 



Incipient 

 Cephalic Tentacle 



Operculate 

 Veliger 



Inflole-shell 

 Veliger 



Cap- shell 

 Veliger 



Trochophore 

 Lorvo 



10 15 20 



TEMPERATURE CO 



25 



30 



Figure 6. — Stages attained by Haliotisfulgens larvae incubated 

 at several temperatures for 15 days. The experiment was ini- 

 tiated with trochophore larvae. 



Circular- 

 Shelled 



Mid Asymmetric — 



Early 

 Asymmetric 



Crawling 

 (Settling) 



Branched 

 Cephalic Tentacle 



Mid Cephalic 

 Tentocle 



Incipient 

 Cepholic Tentacle 



Operculate 

 Veliger 



Inflote-shell 

 Veliger 



Cop-shel I 

 Veliger 



Trochophore 

 Lorwo 



O 5 doys, in as Zygotes 



A 6 days, m as Trochophores 



D 7 doys, in os Operculotes 



10 15 20 



TEMPERATURE CO 



25 



30 



Figure 7. — Comparison of development rate and tolerated 

 thermal range in larvae of Haliotis corrugata placed in the 

 temperature block at 1, 20, and 48 h after fertilization. 



80% within the physiologically acceptable tem- 

 perature range. High mortality near the upper 

 limit might have been due, in part, to oxygen 

 exhaustion. This was tested by sampling open-top 

 tubes in the block at 22° and 24°C for oxygen 

 content after holding approximately 150 larvae 

 (H. rufescens) for 48 h. A decline from 5.8 to 2.9 ml 

 02/liter was observed at 22°C in 48 h. Routinely, 

 therefore, only 25 to 50 larvae or eggs were admit- 

 ted to each tube and once daily tubes were mixed 

 to assure adequate oxygen was available. Subse- 



quently oxygen depletion was not a cause of mor- 

 tality. 



THERMAL TOLERANCE OF 

 POSTLARVAE 



Postlarvae ranging in age from 1 to 2 mo were 

 placed (2-5/tube) in the thermal gradient block 

 and provided each 3-4 days a mixture of three 

 species of diatoms (Nitzschia spp.). Tubes were 

 checked for survival and growth of postlarvae over 

 periods of 2 wk. Survival was good in all species at 

 colder temperatures, but those at 10°-12°C invari- 

 ably were lethargic and could not right them- 

 selves once overturned. Haliotis rufescens 

 survived over the range 10°-19.5°C. Haliotis cor- 

 rugata and H. fulgens were tolerant to the same 

 lower temperatures but had different upper 

 limits, 23.5° and 26.0°C, respectively. Typically 

 survival was nearly 100% over a broad inter- 

 mediate range of temperatures, but declined 

 sharply within 2° of the extremes. 



POSTLARVAL AND JUVENILE 

 GROWTH 



Specific differences in growth rate of both post- 

 larvae and juveniles under laboratory conditions 

 were measured. When its postlarvae were pro- 

 vided near optimal thermal and feeding environ- 

 ments, H. fulgens formed the first respiratory pore 

 in about half the time required by the other 

 species. As the pore is formed, a notch is first seen 

 on the anterior right shell margin. The feature is 

 conspicuous and serves as a convenient point of 

 comparison. The "notch stage" was reached in 

 some rapid-growing H. fulgens at an age of 30 

 days (Table 1). 



Variability in growth rate was marked. Groups 

 of juveniles of identical parentage, age, and rear- 

 ing environment sampled periodically for shell 

 length distribution reflected a broad range and 

 age-increasing standard deviation (Table 2). Shell 



Table 1. — Age and shell length of postlarval Haliotis at forma- 

 tion of the first respiratory pore. 



'Leigtiton, 1972 



1142 



